During a planar scan of a patient with a gamma camera, the gamma camera travels over the patient parallel to the cranium-caudal axis. During ECT scans the gamma camera rotates around the region of the patient to be imaged. The rotation is in a plane generally orthogonal to the cranial caudal axis of the patient and results in the imaging of a cross sectional slice of the patient's body. In either type of scan, it is important that the camera head be maintained as closely as possible to the patient because this results in better resolution and consequently image quality is improved.
In the prior art especially for ECT studies, it is known to use various methods and systems for maintaining the camera head as closely as possible to the patient. For example, U.S. Pat. No. 4,503,331 provides a non-circular ECT scan path. The scanning path is elliptical and accordingly, it more closely follows the body contour than does a circular path.
In U.S. Pat. No. 4,593,189 a camera head is provided with an optical proximity detector to uric the head towards the patient while rotating around the patient. When the head gets too close to the patient, proximity detector is triggered and the head is moved away from the patient.
U.S. Pat. No. 5,072,121 features an arrangement for determining the planar contour of an object using a plurality of light emitters and detectors positioned in a circular planar array. The array surrounds the object for determining the planar contour of the object, such as the patient. The light emitters are sequentially energized and resulting signals from the light detectors are used for determining the object's planar contour. The camera is then directed on a path emulating the contour.
Each of the above patented systems is an improvement over the original circular path used by gamma cameras during ECT scans. Thus, the patent covering the elliptical orbit improves over the circular orbit, but is merely an approximation of the exact contour of the patient's body. Therefore, the distance of the camera head to the patient can be significantly decreased. The proximity detector, among other things, makes it difficult to change collimators in the camera head to which it is attached. The contour determining arrangement of U.S. Pat. No. 5,072,121 requires a learning cycle wherein the system learns the contour of the body. This requires additional time and, therefore, reduces throughput.
It is, therefore, an object of the present invention to provide systems which speed up the scan procedure by automatically positioning the scanning camera as close as possible to the patient's body, even closer than attainable with a prior art elliptical scan, during the scan regimen without necessitating a learning cycle and without endangering the patient.